1. Field of the Invention
The present invention relates to an optical information recording medium and an optical information reproducing apparatus and, more particularly, to an optical information recording medium capable of recording signals on both track guide grooves and lands which are formed into recesses and projections in advance.
2. Related Background Art
In recent years, in optical information recording/reproducing apparatuses using optical information recording media, research and development of high-density recording/reproducing techniques have been enthusiastically made. Conventionally, information has been recorded on track guide grooves (to be referred to as guide grooves hereinafter) or lands between the guide grooves. Recently, however, research and development of a method of also recording signals between the information tracks of a conventional recording medium have been widely made. This method is generally called land/groove recording. This technique is, however, facing the serious problem of how to suppress feedthrough of signals from adjacent tracks (to be referred to as "crosstalk" hereinafter).
A technique of reducing crosstalk by the interference effect produced by forming guide grooves to a depth of about .lambda./5 is disclosed in Japanese Patent Application Laid-Open No. 5-282705.
With regard to address pre-pits, which have the form of recesses/projections, a reduction in crosstalk by an interference effect cannot be expected. For this reason, according to Japanese Patent Application Laid-Open No. 5-282705, address pre-pits are alternately formed in both lands and guide grooves so as not to be adjacent to each other, thereby preventing crosstalk (FIG. 1). As an address pre-pit uses the false reflectivity of a recess, i.e., a change in phase, it has a greater influence on reproduction of an adjacent track than an information recording pit. In this prior art, therefore, no address pre-pits are formed in the guide grooves on both sides of information recording pits 813, and the nearest address pre-pits are address pre-pits 812 and 814 in next lands 802 and 804. With this arrangement, when a laser beam is irradiated on address pre-pits, the address pre-pits in both sides of the information recording pits scarcely affect the information recording pits.
In the above prior art, since address pre-pits are formed in both lands and guide grooves, the manufacturing process for a disk substrate is complicated as compared with a typical recording medium in which guide grooves and guide groove pre-pits or land pre-pits are formed. In addition, in the prior art, there are three different values set in the direction of depth (see the sectional views of FIGS. 2C and 2D), while in a typical recording medium, there are two different values in the direction of depth, i.e., the values of each guide groove portion and each pit portion, and hence the disk substrate itself is very difficult to manufacture. Furthermore, if information is recorded on a track region adjacent to address pre-pits, this information recording region becomes adjacent to the address region. As a result, crosstalk from the pre-pits in the adjacent address region poses a problem in reproduction of the information on the information recording region. If this region is set as an unused region, the recording region decreases accordingly, interfering with the realization of a large-capacity recording medium.